My current setup

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Svilen
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My current setup

Post by Svilen » 07 Jul 2018, 08:45

Just to show you how my setup evolved in the last months and maybe you will have any comments/corrections/ideas to improve the performance?

Driver: GS-1100A2
Detector: Thermo Scientific SPA-3 (2”x2” NaI(Tl) crystal)
Sound card: Aureon XFire 8HD (192 KHz sampling)
Shielding: 3mm copper + 25mm lead

Image

Image

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Background no shielding:

Image

Background inside the lead castle:

Image
Svilen

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Steven Sesselmann
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Re: My current setup

Post by Steven Sesselmann » 07 Jul 2018, 14:53

Svilen,

Nice simple setup, and you seem to be getting nice results, now just a matter of finding some interesting sources and experiments ;)

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

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Svilen
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Re: My current setup

Post by Svilen » 07 Jul 2018, 17:12

Thanks Steven. I want to check it's limits of detecting weak sources now..maybe something like trinitite or slightly contaminated soil.

And something else - the top of the castle is like this because I wanted to complete it with a lighter higher stage (the lead roll I had was 200mm wide and the detector is not fully covered when a sample is underneath). I thought I may roll the flexible material used for patient protection during x-ray, but that seems expensive even used. Now I have an Idea to fill a double sided cylinder with BaSO4, how do you find this idea?

By the way, is there somebody from Europe who can send me a sample of Fukushima soil (I'll pay the expenses of course)?
Svilen

luuk
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Re: My current setup

Post by luuk » 07 Jul 2018, 20:22

Hi Svilen,
I can send you some, give me your address .
Luuk

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Svilen
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Re: My current setup

Post by Svilen » 08 Jul 2018, 05:43

Hi Luuk, very kind from you, thank you! You have a private message with my address.
Svilen

Alain
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Re: My current setup

Post by Alain » 08 Jul 2018, 18:37

Hi Svilen,

Nice results and nice setup:) But I have one suggestion for eventual improviement. I see many DIY shields are 3PI configuration, that means bottom, sidewalls, but no top cover (for easy sample change), and detector from the top. This orientation is exposed to cosmic-rays from above, so background reduction is not optimal. We must know, that cosmic-ray flux is angle dependant: minimum comes from the horizon (angle 0° relative to the horizon), maximum comes from the zenith (angle 90°). So orientation like described above is the worst choice. The amount of vertical cosmic-ray "leak" depends on the solid angle to the sky, which detector "sees". If the hole (well) to the shield is deep and narrow, solid angle will be small (so do cosmic-ray flux), but if the well is wide and shallow, this influence will be higher. The same is valid for the detector position in the well of shield - the higher would it be, more cosmic rays would the detector "see". Try to lay all the setup horizontaly (lean on the desk for 90°) and measure if it is any difference. Of course this position is not always convenient for samples. Optimal would be if you would turn the whole setup for 180° (upside down), but then you must solve problem with holding of detector on place and, the most important, supporting of heavy shield, which must not press with all its weight on the detector. Bottom (now top) should be detacheable, side walls simply fixed to the bottom (on desk , e.g.), sample is then put directly on the detector from above and replace the cover. If you have the possibility to try that, try it and notice if it is any improvement in background reduction.

From high K-40 peak in your background spectra I assume, that you have fairly good shield, or you have much glass in your detector, which is not low-K, or the building material affect this spectra. K is especially high in bricks, made from clay, so in my house, which is made entirely from bricks, the background inside the building is 2-3 times higher than outside and spectral analysis reveals, that K is responsible for that. Because K-40 has so high energy, fighting his line is hard only by making the shield thicker and thicker. It's better to simply escape from it somewhere else;)

Regarding sensitivity: not many people know that you can make a crude caesium "standard" just from common food, which can be found in a market store. Check my post: viewtopic.php?f=5&t=127&p=1970#p1970
Of course, that specifical activity is only approximate, for the very beginning and orientation "where you are", not to be used as an exact reference for every other sample. And it is valid only for this matrix (dried blueberries), density and sample geometry. But it is some estimation anyway, for the beginning, for not being "totaly lost". For potassium it is quite easy: if you have some common potassium compound (KCl, KOH, K2CO3), specific activity can be simply calculated according to molar chemical composition (K content). The woodash is also interesting stuff for calibration. It has both caesium and potassium (at least in my place). If you make a water extract and dry it (so called "potash"), you reduce the mass by factor of 10 (volume even more) and get decent calibration material, which is water soluble, so you can further dilute it and make lower specific activity of the solution at your wish. With this solution you can "spike" other "clean" matrixes and make other check sources (or "standards", if you want). And this way you can test the capability of your detection system, which is measuring its MDA (Minimum Detectable Activity).
If you will need any ash in the future, I can send you. It has approx 1000-2000 Bq/kg Cs-137 (I can measure more accurate value of each "batch", prior its shipment).

Regards,
Alain
Last edited by Alain on 10 Jul 2018, 07:46, edited 1 time in total.
Regards,
Alain

Alain
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Re: My current setup

Post by Alain » 08 Jul 2018, 20:18

Hi Luuk,

Interesting to see that you have Fukushima soil :) Do you have any data (or estimation) of specific activity of Cs-137 in it? I assume this soil is good also for evaluation of the system resolution, because Cs-134 should be still detectable (although 11,8-times lower in activity than at the time of catastrophy) and because Cs-134 peak is very close to Cs-137, resolving those two peaks of very different height is good information about the quality (resolution) of the detector.
Regards,
Alain

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Svilen
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Re: My current setup

Post by Svilen » 10 Jul 2018, 07:33

Thank you for your detailed reply Alain! Upside down would be tricky, but to compare the counts/spectra in vertical and horizontal position of the castle is easy and I can do it. This design is not the best of course, but was a compromise between complexity/price/mass and others. Actually, how significant is the amount of cosmic rays hitting the detector? Do you know what is the frequency and density of secondary cosmic rays per square cm or m ground surface?

About the K-40 - the building is mainly from concrete, don't know how much K-40 in it, but maybe there is enough in the environment anyway. KI i have and 200 grams of it double the counts in the shielding.

Thank you for offering the ash sample, for calibration or not, it will be an interesting source to measure in any case. Isn't 2000 Bq/kg Cs-137 quite a lot? Do you live in an area that could be polluted? According to this article, they measured such activity only from Ukrainian samples: http://www.gamtostyrimai.lt/uploads/pub ... 0befe7.pdf
Svilen

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